1. Field of the Invention
This invention relates to mixtures of nematic-phase liquid-crystals, for use in light shutters and the like, that exhibit the desired nematic phase over a substantial temperature range, preferably one that includes room temperature, as well as a positive dielectric anisotropy.
2. Description of the Prior Art
There are known quite a large number of organic chemical compounds that will, within a particular temperature range, exhibit nematic-phase liquid crystals. These compounds are liquid in the sense that their molecules are neither so dissociated as in a gas nor so tightly bound within a structure as in a solid, but at the same time they are said to be crystalline, in that there is a particular ordering to the orientation of molecules, as is sometimes evidenced by peculiar optical effects. Organic materials exhibit under certain conditions what are sometimes called a mesomorphic phase, and there are different families of organic-chemical compounds that exhibit mesomorphic phases of different kinds--the cholesteric, the smectic, and the nematic. These are each characterized by a particular kind of molecular orientation. For the present, it is enough to understand that most of the known nematic-phase liquid-crystal materials are listed by W. Kast in Landolt and Bornstein, Vol. II, Part 2a, 6th Ed., Springer, Berlin (1960), pp. 266-335. The known materials are not, in the main, suitable for widespread use, since they are nematic only at above about 20.degree. Centigrade or within a temperature range somewhat too narrow to suit them for such use.
It is known that when a nematic-phase liquid-crystal material is stationed between pieces of glass that have been rubbed, each of them unidirectionally and on the surface in contact with the nematic-phase liquid-crystal material, there is thus obtained a liquid-crystal unit whose optic axis lies in a direction of unidirectional rubbing.
The techniques for placing onto flat glass a transparent electroconductive coating of tin oxide or indium oxide or the like are quite familiar to persons skilled in the art of making flat glass. Reference may be made to the patents of Tarnapol (U.S. Pat. No. 2,694,761) or Saunders (U.S. Pat. No. 2,648,752). It is appreciated that if the pieces of glass are to be of relatively large surface extent and evenly spaced substantially throughout same, it is necessary to avoid the development of any appreciable warpage in the flat glass while the transparent electroconductive coating is developed thereon. Though under the technology of about five years ago this presented a considerable problem, since the transparent electroconductive coatings then known were nearly always developed by spraying a tin-containing solution onto glass that was quite hot (about 1000.degree. F.), such that the glass was at about the point of warping, there has recently been made commercially available by a major flat-glass producer a kind of flat glass that is understood to have been produced by vacuum cathode-sputtering onto the glass, while it remains at quite a lower temperature, a composition that is principally indium oxide.
It may be taken as known that there are numerous ways of arranging patterns of luminous, transparent, or opaque material so as to constitute, with suitable selective activation, an alpha-numeric display. It may be taken as known how to supply electrical potential to, and thus activate, patches of electroconductive transparent oxide coating situated on pieces of flat glass.